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Volcanic seafloor vents that roar with the scalding heat of
Earth's interior don't stay hot forever. Eventually, over
hundreds or thousands of years, they flicker out and turn cold.

Yet new research reveals that the action on these
oases of life on the seafloor doesn't stop when the heat
goes off. Life goes on in the frigid dark, but on a teeny scale.

It turns out that large populations of bacteria live on expired
vents, and these microbes are very different from those that
thrive when the vents are piping hot, according to a study
published this week in the journal mBio.

Scientists found evidence that up to
2,000 different sorts of microbes were living in a small
section of a long-expired vent near the East Pacific Rise, a vast
seam on the seafloor in the southern Pacific Ocean where two
tectonic plates are being wrenched apart. For comparison, up to
8,000 varieties of microbes have been found living on active, hot
vents, and up to 10,000 in deep seawater.

Although finding the microbes themselves didn't come as a huge
shock — scientists have found bacteria living in other types of
cool seafloor rocks — the revelation of who exactly moved in once
the vents went cold was surprising, according to the study
authors.

"Seeing the
shift in the microbial population — seeing who actually
came and left was fairly illuminating for me," said study
co-author and geomicrobiologist Katrina Edwards, a professor at
the University of Southern California.

The samples from the East Pacific Rise vents revealed a world of
bizarre biological harmony. Microorganisms that employ utterly
different physiological mechanisms to survive were living almost
side by side.

In
other samples of seafloor rock, the microbe communities
typically change gradually, shifting in a way that brings to mind
a road trip across an entire country, "whereas here, it's like
there are different neighborhoods, and they can change pretty
drastically," said Jason Sylvan, a USC post-doctoral researcher
and lead author on the paper.

Gated communities of anaerobic organisms (which don't need oxygen
to survive) were parked next to gated communities of aerobic
organisms, which do require oxygen.

"Finding things that are anaerobic and aerobic right next to each
other was surprising," Sylvan told OurAmazingPlanet.

A living arrangement akin to a golden retriever and a trout
living across the hall?

"It's probably more drastic than that, but that's the right
idea," Sylvan said.

Big effects

Overall, Edwards said, the research highlights how little we know
about the sheer abundance of
life on the seafloor, which has implications for
understanding large-scale planetary processes.

Both scientists emphasized that the deep ocean increasingly
appears to play a huge role in the way carbon dioxide, a
greenhouse gas that contributes to climate change, is processed
by the planet's interlocking systems of atmosphere, land and
ocean.

"There are all these organisms down there making biomass, and
that's not accounted for in our carbon cycle at all," Edwards
told OurAmazingPlanet. "The ocean floor is quite vast so there is
an opportunity for these organisms to have an effect."

The research comes on the heels of splashy news from deep sea
vents around the world.

Scientists recently announced the discovery of ghostly white yeti
crabs swarming newfound vents near Antarctica, and bizarre shrimp
with eye-like features on their backs that thrive on the
deepest vents ever discovered on Earth.

"When we think of hydrothermal vents we think of things that are
really exciting, like hot, black smoker ventsor big animals," he
said, "but there are also exciting things happening that aren't
necessarily visible to the naked eye."